Light modulating image displays, such as liquid-crystal displays (LCDs) and Liquid Crystal Projectors (LCPs), produce visual images by modulating light provided by illumination element(s). Some such displays have arrays of light modulating elements. Where an image display comprises a plurality of illumination elements arranged at spaced-apart locations, individually controlling illumination elements can improve perceived image quality, for example by providing enhanced contrast.
Separately controlling illumination elements enables spatial variation of the intensity of illumination incident on a light modulator, such as an LCD. Advantageously, spatially varying the intensity of illumination provided to a light modulator may be used to enhance contrast and provide a greater dynamic range of brightness between light and dark areas of an image. Disadvantageously, differences in the illumination provided by different illumination elements may, in some circumstances, result in undesirable visible artefacts, such as haloing.
Example light modulating image displays include the DOLBY® DR37-P display, the SAMSUNG® model LN-T5281F display, and displays described in United States patent applications US 2007/0268577 A1, US 2008/0043034 A1, US 2008/0043303 A1, US 2008/0111502 A1 and US 2008/0074060 A1, all of which are hereby incorporated herein by reference for all purposes.
There is a trade-off between on the one hand, achieving enhanced contrast and dynamic range, and, on the other hand, visibility of boundaries between areas illuminated by different illumination elements. Consider an image comprising a single high luminance local brightness indication, for example a bright white star, on an otherwise low luminance background, for example dark space. Maximum contrast between the local brightness indication and the background would be achieved by controlling illumination elements to maximize the illumination provided to the area of the image that includes the high luminance brightness indication and to minimize the illumination provided to the rest of the image. But controlling the illumination elements for maximum contrast would result in haloing on the low luminance background from illumination produced by the illumination elements controlled for maximum illumination.
There is a need for an illumination element controller that provides high contrast and dynamic range, and minimally perceptible boundaries between illumination elements. There is a specific need for such a controller for providing locally controlled illumination in LCDs and LCPs.